During the processing of pulp suspensions, various processing agents are required to be admixed therewith, for example for heating or bleaching purposes. It is thus desired to disintegrate the agent in the pulp while the pulp is simultaneously transported through a pipe. For heating the pulp, steam is supplied, which condenses and thus emits its energy content to the pulp. During bleaching a bleaching agent is supplied, which reacts with the pulp. In connection with the processing of recycled fiber pulp printing ink is separated by means of flotation, which requires that air shall first be disintegrated in the pulp.
In all of these cases, it is difficult to achieve a uniform admixture of the agent to the material flow with low energy addition. During the heating of the pulp by steam supplied to a pulp pipe problems often arise because large steam bubbles develop on the inside of the pipe. When these steam bubbles rapidly condense, condensate bangs are produced, which cause detrimental cavitation in the pipe and downstream equipment. This restricts the amount of steam which can be supplied to the system, and the desired increase in temperature. It is also difficult to obtain an entirely uniform temperature profile in the pulp. For overcoming these problems, a large amount of energy can be supplied in order to thoroughly admix the steam with the pulp. Another variant is to disintegrate the steam at the point of its supply to the pulp or prior thereto. During admixing of a bleaching agent with the pulp, relatively large amounts of energy are used in order to ensure that the bleaching agent is disintegrated and transported to all of the fibers in the pulp suspension. The energy demand is controlled by the bleaching agent to be supplied (reaction speed) and by the phase of the bleaching agent (liquid or gas). The geometry during the supply of bleaching agent in the gas phase is important in order to avoid undesired separation directly after the admixture. Previous solutions of mixing devices without movable parts have had a limited field of application due to their geometric design and their low mixing efficiency.
One object of the present invention is a novel geometric design to solve the problems with high energy addition, poor distribution of agent, and to avoid the risk of plug formation at the through-flow of pulp suspensions.
The present invention is thus based on the following criteria.
Mixing is transport. The agent can be added at a point where there is a long transport distance to the most remote fibers. This means that a large amount of energy must be supplied for transport to all of the fibers. The agent can be added at one or many points with short transport distance to all of the fibers. This means that low or no energy is required for transport to all of the fibers.
A pulp suspension in the higher concentration range, e.g., from 8% to 18%, cannot be subjected to compression without risk of plug formation. This means high requirements on the geometric configuration of the device.